Spatial and vertical distribution of organochlorine pesticides in sediments from Daya Bay, South China

The spatial and vertical distribution of organochlorine pesticides (OCPs) has been investigated in Daya Bay, China. The concentration of total OCPs in surface sediment range from 16.66 to 44.04 ng/g dry weight with a mean concentration of 26.60 ng/g. DDTs and HCHs were the predominant species. The ratios of (DDD + DDE)/DDT reflected a cocktail input pattern of fresh and weathered DDTs. The predominant α-HCH and the α/β-HCH ratios indicated that the technical HCH contamination was mainly due to historical usage, although there was fresh input of lindane. The variation profiles of concentrations showed that OCPs were extensively applied between the late 1950s and early 1980s in China. A recent increasing trend in concentrations of DDTs and HCHs was found in both cores. The increasing ratios of (DDE + DDD)/DDT with corresponding decreases of DDE/DDT ratio implied that most of the DDTs deposited after their production ban were more likely “weathered” DDTs derived from soil residues.